docker: parse suffixed Docker versions strictly

[Haihan-Jiang]

Fixes #3830. This is a replacement for the closed #3876 with the maintainer feedback addressed.

Docker server versions can be reported with a leading v and build/distribution suffixes such as v20.10.12-v1.0.2. cAdvisor currently parses Docker server versions with the generic unanchored VersionRe, which rejects that form because it finds multiple semantic-version substrings.

This change adds a Docker-specific server-version regexp that:

• requires the version to start at the beginning of the string, with an optional v prefix;
• captures the base major.minor.patch;
• allows an optional suffix after the base version;
• rejects arbitrary text such as random text 1.2.3 and also 9.9.9 build.

VersionRe remains unchanged for kernel-version parsing, so this does not broaden the older generic parser behavior.

Validation:

• GOOS=linux go test -c ./container/docker -o /tmp/cadvisor-container-docker.test
• go test ./container
• git diff --check

Note: container/docker is Linux-only, so on macOS I compile-validated the Linux test binary instead of executing it locally.

[Haihan-Jiang]

This is ready for review. The Docker version parser now handles suffixed versions strictly, with tests around the factory version gating. The visible checks are green.

[github-actions]

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